The present invention relates a heat dissipating structure of a printed circuit board on which a heat generating part is mounted and a fabricating method thereof, and particularly, to a heat dissipation structure thereof improving a heat dissipativity of a heat generating part.
There are conventionally available boards each having a heat dissipating structure to cope with heat generation of electronic parts (heat generating parts) mounted as described below. FIG. 9 is a sectional view of a heat dissipating structure of a printed circuit board in which a through hole is formed and a numeral 1 denotes an electronic part, 2 a though hole and 3 a printed circuit board, which is fabricated by forming the through hole 2, on the inner wall of which a conductor is formed, in the printed circuit board 3 at a site where the electronic part 1 is mounted.
Heat generated by the electronic part 1 is transferred to as far as a conductor constituting a GND surface or heat dissipating fins (not shown) of the lower side of the printed circuit substrate 3 by way of the through hole 2 and dissipated there. A construction is also available in which the through hole 2 is filled with a resin paste with a high thermal conductivity and the resin paste is then cured, thereby transferring heat by way of the resin paste to raise heat dissipativity.
Then, in FIG. 10, there is shown a sectional view of a heat dissipating structure of a printed circuit board having a metal core board, wherein a numeral 1 denotes an electronic part, 30 a conductor layer, 31 an insulator layer and 32 a metal core. A resin or the like is applied as the insulator layer 31 on the metal core 32, on which a circuit made of the conductor layer 30 is formed, thereby fabricating the board including the metal core 32. While the insulator layer 31 is generally made of a resin with a low thermal conductivity, the layer is thin, so that a thermal resistivity can be set to a low value. Heat generated from the electronic part 1 is transmitted through the insulator layer 31 and transferred into the metal core 32 of the board, followed by heat dissipation.
As one of the other examples of heat dissipating structures, there is disclosed a structure which dissipates heat of a part to the rear surface side by way of a high thermal conductivity metal, with a construction formed in a procedure that a through hole in an insulating board at a site where a high heat generating part is mounted is filled with a copper paste and the copper paste is dried and thermally cured to form the high thermal conductivity metal in an embedded state, followed by formation of high thermal conductivity insulating layers on the front and rear surfaces of the insulating board; and further a fabricating method of the structure (see Japanese Unexamined Patent Publication No. 5-259669 (1993), hereinafter referred to as Patent document 1).
In the heat dissipating structure of FIG. 9, a high heat dissipating effect cannot be achieved in a state where the through hole is hollow. In order to obtain a higher heat dissipating effect, the through hole is filled with a high thermal conductivity resin paste or the like. If bubbles and the like are mixed into the resin during filling the resin paste, however, unfilling of the resin and/or voids occur to raise a thermal resistance. Prevention of such inconveniences causes a machine and material, which are expensive, to be inevitably used, resulting in a high cost.
Then, a structure of FIG. 10 can be fabricated more stably than that of FIG. 9 and a heat dissipating effect is also expected to be greater as compared with the structure of FIG. 9 because of a better heat transfer efficiency, whereas the structure of FIG. 10 is costwise higher as compared with an ordinary printed circuit board because of the use of a more expensive material.
In a structure such as shown Patent document 1, since the through hole is filled with copper paste as a high thermal conductivity metal, a possibility arises that bubbles occur in the paste as in the structure of FIG. 9, and in addition, there have been other problems that arise that necessitates steps for forming a high thermal conductivity insulating layer and for drying and thermal curing in the filling for planarization, which complicates both the structure and process.